Production of ferroalloys by mixing in the exclusion of air

ABSTRACT

FERROALLOYS OF THE METALS CHROMIUM, MANGANESE, TANTALUM, NIOBIUM AND/OR VANADIUM WITH A NITROGEN CONTENT OF LESS THAN 0.015% MAY BE OBTAINED BY REACTING A MOLTEN MIXTURE OF RAW STOCK AND LIME WITH METAL-CONTAINING REDUCING AGENTS WHILE POURING THE REACTION MIXTURE FROM ONE LADLE TO ANOTHER IN THE ABSENCE OF AIR, E.G. IN THE PERRIN PROCESS, BY THE USE OF A LADLE HAVING A CLOSED SPOUT ATTACHED TO THE RIM OF THE LADLE OF LENGTH AT LEAST EQUAL TO 1/4 OF THE HEIGHT OF THE SAID LADLE WHEREBY THE LIQUID METAL ALLOY IS POURED FROM THE SAID LADLE UNTO LIQUID SLAG IN A LIKE LADLE.

March 26, 1974 U R 3,799,761

PRODUCTION OF FERROALLOYS BY MIXING IN THE EXCLUSION OF AIR Filed Sept.5, 1971 United States Patent 3,799 761 PRODUCTION OF FERRdALLOYS BYMIXING IN THE EXCLUSION OF AIR Friedrich Breuer, Eschweiler, Germany,assignor to Gesellschaft fur Elektrometallurgie m.b.H., Dusseldorf,

Germany Filed Sept. 3, 1971, Ser. No. 177,694 Claims priority,application Germany, Sept. 5, 1970, P 20 44 143.4 Int. Cl. C21c 5/52 US.Cl. 75-13 9 Claims ABSTRACT OF THE DISCLOSURE Ferroalloys of the metalschromium, manganese, tantalum, niobium and/ or vanadium with a nitrogencontent of less than 0.015% may be obtained by reacting a molten mixtureof raw stock and lime with metal-containing reducing agents whilepouring the reaction mixture from one ladle to another in the absence ofair, e.g. in the Perrin process, by the use of a ladle having a closedspout attached to the rim of the ladle of length at least equal to ofthe height of the said ladle whereby the liquid metal alloy is pouredfrom the said ladle into liquid slag in a like ladle.

This invention relates to the production of ferroalloys of the metalschromium, manganese, tantalum, niobium and/or vanadium, from ores, slagsand/or slag concentrates by the electro-metallotherrnal process, andparticularly relates to a ladle for use in such a process.

Ferroalloys may be produced in conventional manner by reacting a moltenmixture of raw stock and lime with silicon-containing reducing agents,the resultant ferroalloy melt being tapped into moulds in which the meltcools. Ferroalloys thus obtained contain varying contents of nitrogen,particularly when the liquid slag and the ferroalloy obtained by thereduction of the oxide with siliconcontaining reducing agents such asferrosilicon, silicochrome, silicomanganese, has been poured repeatedlyfrom one ladle into another, as for instance in the Perrin process forthe purpose of achieving an improved and more rapid reduction.

When the melt is thus poured from one vessel into another, and also whenit is tapped, a stream of liquid alloy makes contact with the ambientair. Owing to the relativel greater surface of the stream, metals thathave an aflinity for nitrogen, such as chromium, manganese, tantalum,niobium and vanadium, combine with the nitrogen in the atmosphere andthe resultant ferroalloys have nitrogen contents between 0.03 and 0.05%.

Although such nitrogen-containing ferroalloys can be used for theproduction of many steels, the production of special steels having verylow nitrogen contents re- 0 3,799,761 Patented Mar. 26, 1974 Ferroalloyshaving nitrogen contents between 0.005 and 0.01% can be produced in asimple manner by allowing the ferroalloy obtained after the reduction ofthe oxides to cool under the protection of the covering slag which inbulk far exceeds that of the metal alloy. However, this procedure isuneconomical. Due to the protracted cooling times a large number ofladles is needed. The slag that is formed still contains a significantproportion, frequently up to 15%, of unreduced valuable oxides. In orderto recover the metals from such slags these must be remelted, whichincreases the consumption of power.

These disadvantages can be mitigated by a further proposal comprisingthe employment of a two-part divided ladle for reacting the melt of rawstock and lime with the metal-containing, preferably silicon-containingreducing agents. After the completion of the reducing reaction from toof the slag is tapped from the removable upper part of the ladle whichcan hold this quantity, while the alloy in the bottom part of the ladleis allowed to cool under a layer of slag between 5 and 10 cms. thick.The detachable upper part of the ladle from which the slag has beentapped is placed on another prepared bottom part and in this fresh ladlea fresh reaction is performed. By using this arrangement it is possibleto submit the major quantity of the slag to an after-reduction while itis still in the liquid state, since only about 10 to 20% 0f the slag isused as a covering layer for the liquid alloy while this cools. Alloysproduced in such an apparatus contain less than 0.015 and generally onlyabout 0.01% nitrogen.

While the described process permits alloys having the desired lownitrogen contents to be produced, nevertheless during reduction thevaluable action of pouring the slag and the alloy from one vessel intoanother, which in the Perrin process serves for improving andaccelerating the completion of the reaction of the oxide, must becompletely dispensed with.

The present invention allows the advantages of frequent pouring of thereaction mixture from vessel to vessel to be retained, by the use of aladle which has a pouring spout attached to the rim of the ladle, thelength of said spout being equal to at least of the height of the ladle,depending upon the expected volume of slag.

From such a ladle the melt can be poured into another similar ladle insuch a way that the entire metal melt remains under a layer of slagwhich entirely excludes contact with atmospheric air during the processof pouring. This is due to the fact that the liquid metal melt flowsunderneath a protecting layer of slag both in the reaction and in thesecond ladle, the pouring spout of the first ladle being immersed in theslag that has already been poured into the second ladle. The metal thusflows with the exclusion of air from ladle to ladle under the liquidslag.

By using such a particular arrangement according to the invention thepouring of slag and metal melt from ladle to ladle which in practice hasproved to be so beneficial need not be dispensed with and nitrogencontents below 0.015% in the resultant ferroalloys are assured.

The ladle according to the invention may with advantage be fitted with apouring spout at least 10 cms. below the rim of the ladle to ensure thepresence of a supernatant layer of slag that is from to cms. thick whenthe liquid metal is poured out.

Alternatively there may be provided a hood carrying the pouring spout,which is attached to the rim of the ladle so that a collecting chamberis formed which has a capacity calculated to allow the liquid metalalloy to be poured out through the spout under a layer of slag that is 5to 10 cms. thick. The hood is preferably attached to the ladle wall atan angle of about 30 degrees.

Preferably a combination of at least two ladles is used, the rim of theladle which is diametrically opposite the pouring spout being formedwith a recess corresponding to the ladle radius. The ladle that is to beemptied is inserted into this recess to enable the pouring to beaccomplished without trouble and with the retention of a covering layerof slag of about 10 cms. thickness.

A preferred embodiment of a ladle according to the invention isillustratively shown in FIG. 1 of the accompanying drawing, which is avertical section of a ladle according to the invention.

Referring to FIG. 1, attached to the rim 2 of the cylindrical body 1 ofthe ladle is a hood 3 disposed at an angle of 30 which carries a pouringspout 4 extending substantially at an angle of 90 to the vertical axisof the ladle 1. Conveniently the pouring spout 4 may comprise two parts,portion 5 being connected by a flange 6 to portion 4. This serves thepurpose of permitting the end portion 5 which is subjected to greaterwear, to be replaced.

Diametrically opposite the pouring spout 4 the ladle is convenientlyformed with a circular recess 7 radially disposed to the body 1 of theladle.

The capacity of the space covered by the hood 3 and of the outletopening 4 is so calculated that the volume of metal indicated at 8 canbe poured out under a cover of slag which is formed in the ladle in avolume indicated at 9, so that the thickness of the layer of slag abovethe metal 8 as it flows out is between 5 and 10 cms.

The spout 4, 5 has a length selected by reference to the expected volumeof slag 9. In practice the length of the spout 4, 5 corresponds at leastto one quarter of the height of the ladle to ensure that the end of thespout 4, 5 dips into the slag in a receiving ladle when the metal beginsto be poured out.

The ladle according to the invention is designed, in conventionalmanner, to incorporate a crossbar whereby with the aid of the liftinggear of a crane it may function as a tiltable ladle, and preferably acounter weight 13 may be provided near the ladle bottom.

In using the ladle according to the invention, liquid alloy will notmake contact with atmospheric air when slag and metal are poured intoanother vessel, and nitrides do not therefore form.

When the final pouring operation has been completed the principal partof the slag, preferably about 80% of the total volume of slag, is pouredoff into a similar ladle. The residual slag remaining in the first ladleis poured into a cooling mould to a depth of about 10 cms. Afterimmersion of the pouring spout in the liquid slag the liquid metal alloyis also poured in. It will then remain in this mould underneath thelayer of slag until it has cooled to a temperature below 500 C. Whencooling has taken place the slag and the metal alloy may be mechanicallyseparated.

The separation of metal and slag in the liquid state can also beeffected in a manner schematically indicated in FIG. 2, whereby anoverfiow mould 10 is provided between two similar ladles 1 and 1' insuch manner that the volume 11 of metal remains underneath a cover 12 ofslag in the overflow mold while the overflowing volume of slag entersthe second ladle 1'.

If the slag that has overflowed into the second ladle should stillcontain a major proportion of unreduced valuable metal oxides, these canthen be subsequently reduced with metal-containing reducing agents. Whenthis after-reduction has been completed 80 to 90% of the now completelyreduced slag is again poured off and discarded, whereas the liquid alloyand the remaining quantity of slag are added to a fresh melt of rawstock and lime or cooled under the completely reduced slag.

The ladles according to the invention can be used not only for theproduction of ferroalloys that are poor in nitrogen, but also whenevermetal melts are required to be protected from the effects of atmosphericnitrogen or oxygen when being poured from one vessel into another.Naturally it is necessary that a sufficient volume of slag should bepresent during the melting and pouring process.

What is claimed is:

1. In a process for the production of ferroalloys of chromium,manganese, tantalum, niobium, vanadium or mixtures thereof having anitrogen content below 0.015%, from raw stock comprising ores, slags,slag concentrates or mixtures thereof by the electro-metallothermalprocess comprising reacting a molten mixture of raw stock and lime withmetal-containing reducing agents while pouring a reaction mixture of themolten mixture and the metal-containing reducing agents from a firstladle into a second ladle to produce a slag and a liquid metal alloy,the improvement comprising: using a ladle for the first and second ladlewhich has a closed pouring spout attached to the rim of the ladle oflength at least equal to /1 of the height of the ladle to pour aproportion of the total volume of slag from the first ladle into thesecond ladle, allowing the closed pouring spout to dip into the slagcontained in the second ladle, the liquid metal alloy being then pouredthrough the liquid slag to contact the liquid metal alloy with theliquid slag, whereby the liquid metal alloy is poured from the firstladle through liquid slag in the second ladle in the exclusion of airduring the pouring process.

2. A process according to claim 1, in which the closed pouring spout ofthe ladle is attached to the ladle at a point at least 10 cms. below therim of the ladle to ensure the presence of a supernatant layer of slagthat is 5 to 10 cms. thick during the pouring of the liquid metal.

3. A process according to claim 1, in which the closed pouring spout iscarried by a hood attached to the rim of the ladle to provide acollecting space for slag above the opening into the said closed pouringspout.

4. A process according to claim 1, in which the said closed pouringspout is divided into parts detachably connected together by a flangejoint.

5. A process according to claim 1, in which the ladle rim contains aradial recess diametrically opposite the closed pouring spout wherebythe closed pouring spout of the first ladle engages the recess duringthe pouring of metal from the first ladle to the second ladle.

6. A process according to claim 1, in which the pouring process from thefirst to the second ladle is repeated several times.

7. A process according to claim 5, in which after the last pour from thefirst ladle to the second ladle, as determined by the desired completionof the reaction, a major volume of the slag is poured off into a likeladle, and the residual volume of slag remaining in the first ladle ispoured into a mold to a depth of about 10 cms., the pouring spout of thesaid first ladle immersed in the said slag and liquid metal alloy pouredthrough the said slag into the said mold and therein cooled.

8. A process according to claim 7, in which the cooling mould is anoverflow mold interposed between adjacent like ladles.

9. A process according to claim 8, in which after the last pour from thefirst ladle to the second ladle, a proportion of the total volume ofslag is fully reduced in a like ladle with silicon-containing reducingagents to form a metal alloy, removing a proportion of the remainingslag therefrom, and adding the metal alloy formed to a fresh melt of rawstock and lime or cooled in an overflow mold under a cover of slag thatis 5 to 10 cms. thick.

(References on following page) References Cited UNITED STATES PATENTSGlaesner 7546 Dery et a1. 75133 X 5 Willan 266-38 X Wolff 266-38 UXPerrin 7561 X Perrin 7546 Perrin 75133.5

Vdy 751305 6 FOREIGN PATENTS 515,250 11/ 1939 Great Britain 7551 OTHERREFERENCES Allied Property Custodian, Ser. No. 355,846; Perrin;published June 1943, 75133.5.

HYLAND BIZOT, Primary Examiner M. I. ANDREWS, Assistant Examiner US. Cl.X.R. 7546, 61, 130.5

